1. Field of Invention
The present invention relates to valve stem seal assemblies for use in internal combustion engines, and particularly to sealing media applied to metal retainers of such valve stem seal assemblies including bottom flange portions of such assemblies.
2. Description of the Prior Art
Those skilled in the art will appreciate the manner in which intake and exhaust valves are employed in cylinder heads of internal combustion engines. Such valves include integral elongated stems extending away from the engine cylinder heads, the ends of the stems interacting with rotating cams for cyclic repeated opening and closure of the valves during the combustion cycle. The valve stems thus move reciprocally to and from the cylinder head, and so-called valve stem seal assemblies, also variously called oil seal assemblies, are used to seal against leakage of oil through a clearance path between each annular engine valve guide and an associated valve stem supported for reciprocal motion within that particular guide. Obviously, in order to permit unobstructed reciprocal movement of the stem in the guide, some mechanical clearance must exist between the valve guide and the moving stem.
Thus, as is well known, the intake ports of a combustion chamber are opened and closed by the reciprocating motion of at least one intake valve, which in turn is driven by the rotary motion of a cam, the latter being affixed to and rotary with an engine camshaft. The intake valve permits fuel mixed with air to flow into the combustion chamber. In addition, an internal combustion engine has at least one exhaust valve and associated exhaust port for releasing expended combustion gases to the atmosphere. Typically, intake and exhaust valves are of the same construction, and include stems integrally affixed to the valves.
In the typical engine, an oil seal assembly is fitted over each valve stem, each assembly being frictionally mounted over an associated valve guide to assure its securement within the engine. Typically each oil assembly has two primary parts; 1) an elastomeric oil seal positioned at one end to control leakage of oil between the valve stem and guide as noted, and 2) a structural cylindrical part called a retainer which is mounted atop of and frictionally secured to the valve guide. In some cases, the retainer has a so-called lower or bottom flange that extends from the top of the valve guide downwardly to the cylinder head deck.
The cylinder head deck provides support for the bottom flange on which the valve return springs bear. Generally, the spring pressure against the bottom flange is sufficient to deter or otherwise avoid usually minor leakages of oil between the valve guide and the engine cylinder head deck. However, there are some environments that foster significant oil leakage between the normally press-fit interface between the bottom flange and cylinder head deck, e.g. in cases of poor machining or large tolerances.
The present invention deals with the latter situations.
An improved system for sealing between the bottom flange of a valve stem seal assembly and a cylinder head deck of an internal combustion engine is provided. The valve stem seal assembly includes a supporting metallic outer retainer having a lower or bottom-flanged portion, and an interiorly disposed elastomeric seal body bonded to the retainer. The elastomeric seal body includes first and second annular sealing members that engage a valve stem and valve guide, respectively. The elastomeric seal body also includes a third annular sealing member that extends slightly below the bottom surface of the valve guide, as defined by the bottom flanged portion of the retainer, and rests against the cylinder head. Poor machining of the valve guide, and or the cylinder head deck, often creates a leak path for undesirable admission of oil beneath the seal, and through openings between the guide and the cylinder head. The third annular sealing member seals the latter leak path.
The elastomeric seal body also includes axial ribs near the bottom of the retainer, which extend axially toward the cylinder head. The ribs are formed during the manufacture of the valve stem, and represent material left and cured in sprues during manufacture of the part, as will be further explained herein. The ribs are part of the elastomeric seal body, and define outlines of metallic windows disposed between the ribs. Absence of elastomeric material in the window areas represents lower cost of manufacture due to reduced amount of elastomeric material required for manufacture.
Finally, the bottom flange of the metallic retainer supports return springs of a reciprocating valve and stem. The springs assure continuous pressure on the bottom flange, which coupled with the bottom or third elastomeric sealing member, acts to prevent leakage of oil between the flange and the cylinder head deck.